1. Field of Invention
This invention relates in general to a process for fabricating electrophotographic imaging members.
2. Description of Related Art
Typical electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated, for example, in U.S. Pat. No. 4,265,990, incorporated herein by reference in its entirety. The 990 patent describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer.
Generally, where the two electrically operative layers are supported on a conductive layer, the photogenerating layer is sandwiched between the contiguous charge transport layer and the supporting conductive layer. The outer surface of the charge transport layer is normally charged with a uniform electrostatic charge. The photosensitive member is then exposed to a pattern of activating electromagnetic radiation, such as light. The activating electromagnetic radiation selectively dissipates the charge in illuminated areas of the photosensitive member, while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image, by depositing finely divided electrostatic toner particles on the surface of the photosensitive member. The resulting visible toner image can be transferred to a suitable receiving material, such as paper. This imaging process may be repeated many times with reusable photosensitive members.
As more advanced, complex, and highly sophisticated, electrophotographic copiers, duplicators and printers have been developed, greater demands have been placed on the photoreceptor to meet stringent requirements for the production of high quality images. For example, to provide excellent toner images over many thousands of cycles, the numerous layers found in many modern photoconductive imaging members must be uniform, free of defects, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits. One type of multilayered photoreceptor that has been employed, in drum or belt form, in electrophotographic imaging systems comprises a substrate, a conductive layer, a charge blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers, such as an overcoating layer.
Excellent toner images may be obtained with this and other multilayered photoreceptors. However, it has been found that the numerous layers limit the versatility of the multilayered photoreceptor. For example, when a thick, e.g., 29 micrometer, charge transport layer is formed in a single pass, a xe2x80x9craindropxe2x80x9d pattern forms on the exposed imaging surface of the final dried photoreceptor. This is discussed in detail in U.S. Pat. No. 6,214,514 to Evans et al., which is incorporated herein by reference in its entirety. This xe2x80x9craindropxe2x80x9d phenomenon is a print defect caused by high frequency coating thickness variations in the relatively thick (e.g., 29 micrometer) charge transport layer. More specifically, the expression raindrop, as employed herein, is defined as a high frequency variation in the layer thickness. The spatial period of this variation is in the 0.1 cm to 2.5 cm range. The amplitude of this variation is between 0.5 micrometer and 1.5 micrometer. The xe2x80x9craindropxe2x80x9d variation can also be defined on a per unit area basis. The raindrop defect can occur when the transport layer thickness variation is in the range of 0.5 to 1.5 microns per sq. cm. The morphological structure of raindrop defect is variable and depends on where and how the device is coated. The structure can be periodic or random, symmetrical or oriented.
U.S. Pat. No. 6,214,541 discloses a process for fabricating electrophotographic imaging members including providing an imaging member including a substrate coated with a charge generating layer having an exposed surface, applying a first solution including a charge transporting small molecule and film-forming binder to the exposed surface to form a first charge transporting layer having a thickness of greater than about 13 micrometers and less than about 20 micrometers in the dried state and an exposed surface, and applying at least a second solution having a composition substantially identical to the first solution to the exposed surface of the first charge transportation layer to form at least a second continuous charge transporting layer, the at least second charge transporting layer having a thickness in the dried state of less than about 20 micrometers, the at least second charge transporting layer, and any subsequent applied solution having a composition substantially identical to the first solution.
Although this is considered an acceptable solution, it results in an extra coating pass leading to higher manufacturing costs.
This invention provides systems and methods for fabricating an electrophotographic imaging member having reduced raindrop variation.
This invention separately provides systems and methods for achieving coating uniformity in a single charge transport layer formed in a single pass.
This invention separately provides systems and methods for reducing raindrop defects in single charge transport layers formed in a single pass.
The systems and methods for fabricating electrophotographic imaging members according to this invention comprise forming an imaging member having a substrate coated with a charge transport layer, where the material used to form the charge transport layer has a viscosity of about 1500-2100 cps.
If desired, after forming the charge transport layer, the resulting electrophotographic imaging member may optionally be coated with any suitable known or later-developed overcoating layer.
Other layers, such as conventional ground strips comprising, for example, conductive particles dispersed in a film-forming binder, may be applied to one edge of the multilayer photoreceptor and in contact with the conductive surface, blocking layer, adhesive layer or charge generating layer.
In various exemplary embodiments, a back coating layer may be applied to the side of the substrate opposite the multilayer photoreceptor to provide flatness and/or abrasion resistance. This back coating layer may comprise an organic polymer or inorganic polymer that is electrically insulating or slightly semi-conductive.
The multilayer photoreceptor manufactured according to this invention may be employed in any suitable conventional or later-developed electrophotographic imaging process which utilizes charging prior to imagewise exposure to activating electromagnetic radiation. Conventional positive or reversal development techniques may be employed to form a marking material image on the imaging surface of the electrophotographic imaging member of this invention.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.